1. Field of the Invention
This invention relates to a split type internal combustion engine including a plurality of cylinders split into two groups and operating in a split cylinder mode where one group of cylinders is supplied with fuel and fresh air and held operative and the other group of cylinders is supplied with neither fuel nor fresh air and held inoperative when the engine is under low load conditions.
2. Description of the Prior Art
Generally, internal combustion engines exhibit higher fuel combustion and thus higher fuel economy when running under higher load conditions. In view of this fact, split type internal combustion engines have already been proposed as automotive vehicle engine or the like which are subjected to frequent engine load variations. Such split type internal combustion engines are designed to have a plurality of cylinders split into first and second groups which communicate with the intake passage through first and second separated intake manifolds, respectively. Under low load conditions, the first group of cylinders is supplied with fuel and fresh air and held operative while the second group of cylinders is supplied with neither fuel nor fresh air and held inoperative to increase relative loads on the first group of cylinders for high fuel economy. In addition, exhaust gases are re-introduced into the second intake manifold to suppress pumping loss in the second group of cylinders for further high fuel economy.
One difficulty with such split type engines is that a portion of the exhaust gases re-introduced and present in the second intake manifold during a split cylinder mode of operation, flow into the first intake manifold to spoil fuel combustion in the first group of cylinders when the engine is shifted from its split cylinder mode to its full cylinder mode. Additionally, a portion of exhaust gases re-introduced into the second intake manifold flows into the first intake manifold to spoil fuel combustion in the first group of cylinders temporarily when the engine is shifted from its full cylinder mode to its split cylinder mode.